High-frequency apparatus



July l2, l949- L. E. THOMPSON HIGH-FREQUENCY APPARATUS 4 Sheets-Sheet 1 Original Filed Feb. 6, 1945 ATTORNEY L. E. THOMPSON HIGH-FREQUENCY APPARATUS 4 Sheets-Sheet 2 July l2, 1949.

Original Filed Feb. 6, 1945 July 12, 1949 L. E. THOMPSON HIGH-FREQUENCY APPARATUS Original Filed Feb. 6, 1945 4 Sheets-Sheet 3 v July l2, 1949. L. E. THOMPSON HIGH-FREQUENCY APPARATUS 4 Sheets-Sheet 4 Original Filed Feb. 6, 1945 kbl Patented July 12, 1949 HIGH-FREQUENCY APPARATUS Leland E. Thompson, Merchantville, N. J., alsignor to Radio Corporation of America, a oorporation of Delaware Original application February 6, 1945, Serial No. 576,453. Divided and this application March 15, 1946, Serial No. 654,553

4 claims. (Cl. 332-25) This is a division of my co-pending application Serial Number 576,453, filed February 6, 1945, entitled Radio relaying.

In my copending parent application referred to, I have described an ultra short wave radio relaying system making use of an ultra short wave oscillation generator. This oscillation generator is of the type making use of a cavity resonator having a gap, oscillations being produced in the resonator by an electron discharge system including a negatively charged anode, a positively charged grid and a cathode.

An object of my present invention is to provide improved circuit arrangements for frequency modulating the output of such a high frequency oscillation generator. A further ob- .ject is to provide improved circuits for automatically frequency controlling the same. Other objects, advantages and features will appear with the more detailed description of my present invention.

In the accompanying drawings- Figure 1 illustrates schematically a transmitting terminal for an ultra high frequency relay system. The terminal makes use of a high.

quality voice channel having, as indicated, an upper frequency of 10,000 cycles although if desired this may be raised to 15,000 cycles and several other signaling channels which are transmitted to a common amplier as side bands of suitable sub-carriers. All of the signals are combined, pre-emphasized in a suitable network and used to frequency modulate a common sub-carrier having, as illustrated, a mean frequency of one megacycle. The latter, in turn, is used to frequency modulate a transmitted carrier having a mean frequency of 3,000 megacycles.

Figure 2 is a block diagram of a relay station for use with the transmitting terminal of Fig. 1. It will be noted 4that the received doubly modulated Waves are converted to a suitable intermediate frequency, amplified, and then subjected to a single frequency demodulation. 'I'he waves resulting from this single frequency demodulation are then used in part for purposes of automatic frequency control of the local beating oscillator and to frequency modulate a new locally generated carrier.

Figure -is a schematic showing of a high frequency oscillator and circuits therefor for utiliz- 4ure 2.

Figures 4 and 5 are different cross sectional shapes which the cavity resonators may take for use in Figures 3 and 6, and Figure 6 is a more detailed schematic diagram of the first local oscillator and converter employed at a relaying point such as Figure 2 or at the terminal receiver such as shown in my parent application. Figure 6 also illustrates circuits for automatically frequency controlling the first beating oscillator.

In Figure 1, several independent signaling channels are combined and modulate the waves radiated from the transmitting antenna TA to the receiving antenna RA200 of the relay station of Figure 2. The waves received at the relay station are heterodyned, amplified, detected and used to modulate a difl'erent carrier frequency wave. The latter is radiated over the relay transmitting antenna TA2|4 to the receiving antenna of a terminal station. f

Turning more specifically to Figure 1, the signal channels are designated by the letters A to F, inclusive. These channels are combined in resistor 23 and fed through transformer 24 and pre-emphasing network PN in order to oppositely frequency modulate oscillators 25 and |02.

Oscillator 25 may operate, by way of example, at an unmodulated frequency at 10 megacycles and oscillator |02, for example, at an unmodulated frequency of 11 megacycles. The outputs ofthe two oscillators 25 and |02 are combined in the converter |00 as a result of which the frequency .modulation appearing in the peak frequency output of converter |00 is equal to the sum of the deviations of the oscillators 25 and |02 when they are caused to separate in frequency.

The deviation ratio of the modulated waves appearing in the output circuit of the second frequency modulated oscillator |04 is unity or more, as desired, as a result of which the waves radiated over the transmitting antenna TA have for maximum deviation, a frequency of 3000 megacycles plus and minus 1.0 megacycles. A larger deviation ratio .may be used, in which case airfares 3 the radiated waves would be, for example. 3000 megacycles plus and minus 2, 3, ormore megacycles when fully modulated.

The waves radiated from the transmitting antenna TA of Figure 1 may be received directly by receiving apparatus as shown in my parent application. Ordinarily, however, such waves would be radiated to the receiving terminal by way of one or more relaying points, such as illustrated in Figure 2. The waves would be received at the relay point at one frequency and re-transmitted to the next point in the system at some diiferent frequency so as to avoid feedback or singing at the relay station.

In the relaying system illustrated in Figure 2. the waves are pickedv up or received on a receiving antenna RA200. down in frequency in a converter circuit202 with waves from a local beating oscillator 204. The intermediate frequency produced may be 30 megacycles plus and minus 1.0 megacycles. The waves of intermediate frequency are amplied in an intermediate frequency amplifier 206` and then fed to a discriminator detector 200.

The action of the discriminator detector is such as to produce a wave of one megacycle plus and minus 1'70 kilocycles corresponding to the output of the converter of Figure 1. This wave is limited and amplified in appropriate apparatus 2|0 and then used to frequency modulate oscil- The received waves are beat` an evacuated container 600 which may be of vglass or metal, within which are contained a heated cathode 60|, a screen electrode diagrammatically illustrated in section at 600, a cavity resonator 604, and a' disc-like metallic anode or electron receiving plate 505. The cathode 50| is externally grounded at 602. The cavity resonator 604 is made of metal and consists of a metallic cylinder 606 having metal bases 501, 608. Mechanically and electrically fixed to the bases are the internally protruding sleeves or tubes 600, 6|0 separated so as to have between them a gap 6| The tube 600, cavity resonator 604, sleeves 600. 6|0 and plate 605 are shown in cross section.

Actually, the cavity resonator may have dii.'- ferent dimensions and be proportioned differently than as shown in Figure 3. The distance between the bases 601, 608 may be equal to or less than the internal diameter of the cylinder 606, as shown diagrammatically in cross-section in Figure 4. Also, the bases may be dished in and the cavity resonator have the toroidal or doughnut shape shown 1n cross-section in Figure 5.

lator 2|2 whose unmodulated frequency may be r 3010 megacycles. I

By adjusting the amplitude of the output of amplifier 2|0 the waves radiated over the transmitting antenna TA2|4 of the relay point of Figure 2 may be made 3010 megacycles plus and v l minus 1.0 megacycles.

Also it is to be noted that allofthe channels need not be voice channels, but, if desired, some of them may be telegraph channels, some voice and some of other types, such as facsimile and teletype channels. Thus, as a possible alternative -channel A may be replaced by twelve telegraph channels, the separate telegraph carrier tones of which may occupy the band from 465 to 2295 cycles, each tone channel having a width of 170 cycles. Thus, the rst telegraph channelmay be designed for a tone carrier of 465 cycles with a signaling width of plus and minus 85 cycles, the second tone channel may use a tone carrier of 595 cycles with a cycle width of plus and minus 85 cycles, etc.

In addition to channels A-F inclusive, of Figure l, a service channel SC may be provided. The output of theservice channel pick-up microphone may be amplified by the service channel amplier -SCA and switched directly, by means of switch SCS, to frequency modulate oscillator |04; Preferably, amplifier SCA passes a band of .approximately 05000 cycles and the amplitude of the modulating voltages is adjusted so as to produce, for example, a maximum swing of :15,000

cycles in the output of oscillator |04.

The anode 605 of Figure 3 is maintained at a negative potential of the order of -150 volts with respect to ground by means of lead SI2 connected through'resistors 6 3 and 6|4 to a suitable source of potential 6|5 by-passed ,to ground by means of the by-passcondenser 6|6. The cavity resonator 604, together with the grid 603 connected thereto, is maintained. at positive potential of the order of +300 volts, for example. with respect to ground by means of lead 6|1 connected to a'suitable 6|6 by-passed by condenser l source of potential 619.

As a resultof the foregoing construction, electrous emitted from the cathode cuiy are-attracted. to and pass through the hollow portion of ytubes 609 across gap 6|| and-through tube'6'i0." 'Ine electrons .then `approach the negatively charged anode 605 only to be repelle'dj` and attractedb'ack y across they gap 6| Invthis'v-waypthe. cavity re-; sonator 604.4 is yexcited ,i so *that*l'iighfrequency'A waves are set up therein at a' frequencydeter` mined, in the main,v by -the cubical'contentof the cavity resonator 604.'lhe frequency of --operaj-j tion'isalso dependent, toa,v certain extent, upony the'voltages appliedtothe various oscillator elements.

Output energy vis l,tal-ren -fromvresonator-60'4 by means of conductor 620 lcoupled.,by means of the v transmitting antenna TA fof Figure 1 or the relay As indicated in Figure 2 the'service channel f band may be filtered out by filter SCF and taken from line SCL for use in earphones, or the output of line SCL may be fed by patch cords to the service line input SLI to modulate oscillator 2|2.

In Figure 3 there is shown a form of high frequency oscillation generator which is used at |04 in Figure 1 and at 2|2 in Figure 2. Figure 3 also illustrates circuits especially adapted fo'r producing frequency modulation of the high frequency oscillator |04.

The oscillation generator ci' Figure 3 comprises inductiveloop'Gzl, tothe space withinthe cavity y resonator 604. Conductor 620 is suitably shielded j by means of the externally' grounded' metallic .o

coaxial' conductors '62|A, 622.. Thel highvfrequency conductorl 620 leads tofand-excites-the retransmitting antenna TA,2|4 of Figure 2.`

When the oscillator in Figure 3 is used inthe transmitting arrangement of Figure 1, it is modulated by the output of the converter orr mixerl |00 of Figure 1. The output vof Aminer |00 rvis fed through Aconductor |0|a to the anode circuit of anode 605 of Figure 3. In the case of the'trans-v mitter of Figure 1 conductor |0|a will carry a frequency modulated wave of one megacycle having a maximum frequency deviation of fi'- 170 kilocycles, according to the example chosen. v s.

The waves in conductori 0 I a, referring to 'Figure 3, are resonated in the parallel tuned circuiti!) vcomprising coil 624,-.tovwhich conductor |0I-afis g variably tappedat tapping point 625, andcondenser 626. The tuned circuit 623 is broadened by the use of I a 'loading' resistor 621 connected in shunt tothe circuit. By mean of variable condenser 628, the frequency modulated waves apamounts, to the plate 605. As a consequence, the output of the oscillator of Figure 3, appearing in lead 620, is frequency modulated to an extent which may be controlled primarily by adjustment of condenser 628,'and secondarily by adjustment of tap 625.

Since the negative voltage applied to the lead 6|2 is fed through resistors 6|3, 6M which may, by way of example, be 22,000 and 180,000 ohms in value, respectively, leakage of the waves appearing in circuit 623 to ground through lead 6|2 is eifeotively prevented. l f

For monitoring and adjustment purposes, a portion of the high frequency waves fed through condenser 628 tothe plate 606 may be shunted through high frequency by-passing condenser 629 to switch 630. The latter, in its upper contact position 63| feeds the'rectier 632 to the output of which is connected a suitable meter 633. The rectied output of rectier 632 will indicate the voltage applied to plate 605 and will be a measure of the frequency deviation in the oscillations generated by the oscillation generator and fed to the output transmission Iline 620.

The service channel is fed 'throughswitch sos of Figure 3, ,which corresponds to switch SCS of Figurel, across -a potentiometer634. For'modulating the .high frequency oscillator of. Figure 3 with theiservice .channel voltages,l .the latter are fed through tap 635, vaudio frequency by-pass conv denser 636, across resistor 6|4 and through resistor 6|3 and lead 6|2 to the anode 605 ofthe oscillation generator. By throwing switch 630 to the lower position 631, the extent of the frequency modulation produced by the service channel may then be measured by noting the reading on meter M which will then be actuated by rectified service channel voltages. For aurally monitoring the service channel an amplier 638 and earphones 639 are provided, asl indicated.

It is again repeated that all values of frequencies, resistances, voltages, etc. are given as illustrative or typical only and, therefore, it is to be clearly understood that all inventions described herein with reference to vall figures of thel drawings are not to be restricted to such values.

In Figure 3 the filament heating voltage source for cathode 60| is illustrated to be a battery but this battery may-be replaced by a transformer supplying suitable alternating voltages to the filament for heating the cathode to an electron emissive condition. Also, the sources 6|0 and SI5 for the cavity and plate maybe replaced by potentiometers supplied with rectied commercial 60 cycle current. Such alternating currents for exciting the filament an-d the ripple in the rectified voltages may produce 60 cycle and 120 cycle frequency modulation of the output of the oscillator of Figure 3. This hum Will therefore appear in the service channel. It will not appear, however,

in the high quality channel A or in the channels B to F inclusive, since such low frequency modulation is effectively filtered out by the selectivity of the subcarrier circuits in the receiver.

This filtering action follows since there is a substantial separation in frequency between the first significant side bands produced by the sub-carrier in the output of the oscillator of Fig. 3 and the side bands produced by vthe low frequency power modulation. Therefore the power supply hum and mechanical vibration modulates the carrier, but not the subcarrier. The signal channels A to F receive only the modulation of the subcarrier. The low frequency power modulation is produced by the 60 cycle heating supply or harmonics of 60 cycles representing ripple in the rectified power supply. This undesired low frequency modulation may also be produced by undesired mechanical vibration.

It isto be noted that oscillators of the typey shown in Figure 3 are peculiarlysusceptible to this low frequency type of frequency modulation due to mechanical vibration or the use of imperfectly filtered rectified power or due tothe use of valternating current operation of the cathodes. It-

of circuit so that across resistor 2l, only voltage from channel A or amplifier 0 would be set up. Channel A would be adjusted so as to produce a full deviation'of plus and minus 170 kilocycles .in the output of converter |00. This simplex high quality signal could be radiated directly to receiving apparatus or relayed thereto through the apparatus of Figure 2.

nator 604 and. may be controlled 'by providing suitable externally operatedmeans for warping of the sides of the cavity reso'nator 604 so as to change its internal volume. Also, the frequency may further be controlled by adjustment of the voltages applied to the electrodes of the oscillator. I v

' Figure Gillustrates in greater detail the beating oscillator-converter apparatus designated schematically at 202 and 204 in Figure 2. That is, the receiving antenna RA-200 of Figure 2y is connected to the transmission line 100 of Figure 6. Line 100 is provided with an externally metallic shield 102, grounded at 104. Also, transmission line 100 is terminated by an kinductive loop 105, thereby establishing coupling within the cavity resonator 106. If desired, transmission line 100, 102 may be replaced. by a wave chute or guide. l'

The cavity resonator 106 is of metal and cylindrical in shape. Extending within the resonator 106 and connected to one of its bases is cylindrical line section 190 whose base 16| is adjacent and spaced from the metal circular', base 192 carried by metal bellows 1|I. The line section 190 is tuned by means of this cylindrical metallic bellows 1|| having, as indicated, springy corrugated side walls. By means of the bolt 1| 3 and nut 1|5, the capacity between plates 19| and 192 is adjusted as is also the volume or internal cubical content of the resonator. Preferably the line section 190 is approximately one quarter wave length long-here about 3/4 of one inch. Thisline section is tuned by adjustment of plate 192 to the frequency of the waves received and fed in at 105. A crystal detector 108 is mounted as shown with one terminal 196 in electrical contact with 106 and its other terminal 196 protruding through opening 191 in the cylindrical line section 190. Terminal 166 is connected to conductor or line 1|0. As a result, the crystal detector rectiiles the waves fed in at and 1|8 and feeds the resulting difference4 frequency of about 30 mc. into line 110.

The frequency of operation of the oscillator of i Figure 3 is determined by the dimensions of resohighfrequency oscillations by means of a capac-vk ity end plate 1|8 xed to an exposedsection of transmission line '|20 protruding within the reso.. nator. The'line 128 is excited by an automatically frequency controlled high frequency oscillator y operating in the neighborhood of either l3030 megacycles or 2070 megacycles. The oscillator will be described more fully later.

The beat frequency is fed through line 1I0` shielded by the external conductor 1 I2 to the primary 1I6 of a transformer whose secondary coil 126 is tuned by condenser 126. The output of the tuned circuit 126, 128 is fed through line 132 to the first stage of theV intermediate frequency amplifiers and limitersv206 of Figure 2.

The high frequency oscillator 138 of Figure 6 operating in the neighborhood of 2070 megacycles or 3030 megacycles is similar in all essential re-l spects to the high frequency loscillator 600 of Figure 3.

In Figure 6, the oscillator comprises an evacuated container 138, a cathode, 134, grounded at 136, a negatively biased plate 156, Aa positively charged cavity resonator 142 and a grid 144 connected to the resonator. The resonator 142, shown l in cross section, is cylindrical in shape and is made of metal. The resonator has metallic bases 152, 154 which are perforated and to which are at` tached the hollow metallic tubes 146, 150. The tubes 146, 150 are separated at an intermediate point so as to provide a gap 148. In a way similar to that explained in connection with Figure 3, oscillations are set up in the cavity resonator 142 of Figure 1 and wave output is derived from the inductive loop 148 coupled tothe space within the cavity resonator 142.

The external surface of the cavity resonator '|06 is grounded at 104 as indicated.

By properly choosing the dimensions of the cavity resonator 142 and by appropriate adjustment of the voltages on the elements of the oscillator, oscillation' at a desired frequency may be had. As beforeindicated, by suitable external means the shape of resonator 142 may be warped so as to change its cubical content and, hence,'its frequency of operation. Or, if desired, ametallic bellows adjustment, such as that provided for the cavity resonator 106 fmay be provided for 142, but in this case, of course, the container 138 should be hermetically sealed to resonator 142 so that av` portion of its external surface containing andVV otherwse su ortin the metallic bellows struc.- v

l pp g whereby oscillations are produced by electron [flowacross` said gap, a tuned circuit connected '..to Lsaid. 'ano'de"'through a variablewimpedance, -means coupled to said tuned circuit at a location ture would be exposed for external adjustment.

The output appearing in the tuned circuit`.1 26,.. 128 would be, for the example chosen, a wavev as indicated in Figure 2 having a mean frequency 'A of 30 megacycles and maximum frequency deviaf tion of :1.0 megacycles. This wave is fed to the intermediate frequency amplifying, limiting andA discriminator detector stages.

The discriminator detector' of Fig. 2 is also schematically in` Figure 6 in connection withv ,vacuum tube 160. More specifically. a source of .voltage 165 is connected vacross the leads .or ter-` minalsg116, 118 and these terminals areconnected toaA potentiometer 114. kBy properly adjusting the tap'112 on potentiometer 114, and by'proper choice of values for other circuit elements, the current flow through, orl the conductivity vof tube 160having the anode 162, grid '164, the cathode 168, `may be controlledso that the voltage applied through lead 158 upon the plate 156 is of a desiredvalue, such as', for example, -150 volts. As vindicated, the plate lcircuit for tube `'|60 is returned to ground vthrough a resistor 16| shunted by condenser 182 and through the ground connection 163 tothe source of potentialsv 165. It should,v therefore, be clear that the automatic frequency controlling voltages appearing across resistors 182 and 184 will vary lthe current flow through the tube 160 and hence its effective resistance. ConsequentlyVthe voltage in lead 166 will vary in such a way as vto control of the IFA system 206 of Figure 2.

I claim: y l. High frequency apparatus comprising a Cav? y ity resonator having a gap, anegatively charged anode located on one side of said gap, an electron emitting cathode on theA other side of said gap, ya' circuit for maintaining said resonator at a positive potential with respect to said `cathode whereby oscillations are produced by electron flow across said gap, a tuned'circuit connected to said anode, apparatus for .producing high frequency waves in said tuned circuit whereby the oscillations produced in-v said -cavity resonator arefrequency modulated in accordance with the high frequency oscillations in said tuned circuit, and apparatus for adjusting the coupling of said tuned circuit to said anode in order to control the amount 'of' frequency modulation in the oscillations within said cavity resonator. l

2. Apparatus as claimed in the preceding claim, characterized by the fact that said adjustablev coupling consists of a variable condenser.

3. High frequency apparatus comprising a cavityresonator having a gap, a negatively charged Aanode'located on Aone side of said gap, an electron emitting vcathode' on the other side of said gap, a circuit f ormaintaining said resonator at diagrammatically illustrated at 208 in Figure` across the output terminals of which are vconnected resistors 182, 184, which, as will be explained more fully quency controlling voltages. These then be usedto control the frequency of oscillator 138 so as to maintain the beat frequency waves within the pass band of intermediate frelater, provide automatic fre,-

voltages may a positive potential with respect to said cathode eifectivelydntermediate its ends for supplying fre-v quencymodulated signals thereto, to thereby exthe coupling of Asaid tuned circuit to said anode `inA order to control the amount of frequency modulation in the oscillations within said cavity resquency amplifying and limiting stages 206 of` f Figure 2.

The frequency controlling circuit for the oscillator 138, from which .the automatic frequency controlling voltages are derived. is illustrated onator.

4. High frequency apparatus comprising a metallic cavity resonator having a gap, cathode and velectron repeller electrodes on opposite sides of said gap, a source of unidirectional potentialiconnectedto said resonator, av source -of unidirectional `potential connected vto said repeller electrode through a resistor, said sources maintaining said resonator and repeiler electrode at potentials of different polarities relative to said cathode.. a. parallel tuned circuit of inductance and capacitance connected between said repeller electrode and said cathode, a loading resistor in shunt 5 to said tuned circuit, a source of frequency modulated waves adjustably connected to a point on 4the inductance of said tuned circuit, and an adjustable element in circuit with said tuned circuit for varying the degree of coupling of said tuned circuit to said repeller electrode. and an output circuit coupled to said resonator, whereby the extent of frequency modulation produced in said resonator. is controlled cy both adjustable connections.

LELAND E. THOMPSON.

0 REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

